1. Field of the Invention
The present invention relates to a development roller used for copying machines, facsimiles, printers or the like, more specifically to a development roller which includes a development sleeve disposed adjacently to a photo conductive drum and a magnetic roller disposed in the development sleeve and in which a developer including a toner and a magnetic carrier is adsorbed to an outer surface of the development sleeve by a magnetic force of the magnet roller, a surface treatment device configured to treat the outer surface of the development sleeve, and a wire member used to roughen the outer surface of the development sleeve.
2. Description of Related Art
Various development devices as disclosed in, for example, Patent Documents 1 and 2 are used for image forming apparatuses such as copying machines, facsimiles, printers or the like. As shown in FIG. 7, the development device 100 of this kind includes a development roller 104 which is configured to feed a developer 101 including a toner and a magnetic carrier to a development area 103 facing a photo conductive drum 102 and develop a latent image formed on the photo conductive drum 102 by the developer 101 to form a toner image on the photo conductive drum.
The development roller 104 includes a development sleeve 105 which has, for example, a cylindrical shape, and a magnetic roller 106 which is disposed in the development sleeve 105 and configured to generate a magnetic field to form raised portions, or ears of the developer on a surface of the development sleeve 105. Here, the magnetic roller 106 has, for example, a cylindrical shape. The magnetic roller 106 has a plurality of magnetic poles which comprise bar-like magnets. Of the plurality of poles, development poles facing the development area 103 are configured to form the ears of the developer on the surface of the development sleeve 105 and supply the toner of the developer to the photo conductive drum 102.
When the developer 101 rises to form the ears, the magnetic carrier of the developer 101 is raised on the development sleeve 105 along magnetic lines generated by the magnetic roller 106. The toner of the developer 101 is adsorbed to the raised magnetic carrier. In addition, the development roller 104 is configured to feed the raised developer 101 to the surface of the development sleeve 105 by rotating at least one of the development sleeve 105 and the magnetic roller 105.
Generally, the above-mentioned development roller 104 is configured to rotate the development sleeve 105 in order to facilitate the feeding of the developer 101. In the development roller 104 shown in FIG. 7, the development sleeve 105 is configured to be rotatable by attaching a flange to an end of the development sleeve 105 and supporting the flange by a bearing. The development sleeve 105 is disposed close to the photo conductive drum 102 and a control member 107 to control an amount of the developer 101 fed to the photo conductive drum 102.
Moreover, the above-mentioned development sleeve 105 (in particular, see Patent Document 4) has an outer surface on which sand blast processing or roughing treatment is provided, or in which V-shaped grooves or concave grooves are provided to convey the developer to the photo conductive drum certainly.
If a rotational center of the development roller 105 deviates from an axis, wobble of rotation of the development sleeve 105 occurs. The generation of the wobble of rotation of the development sleeve causes a gap between the control member 107 and the photo conductive drum 102 to vary to generate variation in an amount of the developer 101 supplied to the photo conductive drum 102, thereby generating variation of density in a formed image. Therefore, the above-mentioned development device 100 is configured to match the rotational center of the development sleeve 105 with the axis as much as possible, maintain straightly the axis as much as possible and maintain a shape in section of the development sleeve in a constant perfect circle so that the wobble of rotation of the development sleeve does not occur to obtain a high quality image.
On the other hand, there is known a surface treatment device to roughen an outer surface of a supplying member such as a development sleeve of a development roller to convey a developer attached to the supplying member to a photo conductive drum (for reference, see Patent Documents 6 to 9). The surface treatment device is configured to contain the supplying member and abrasive grains in a containing tank, generate a rotational magnetic field to move the abrasive grains, excite the abrasive grains randomly by an electromagnetic force operating between the rotational magnetic field and the abrasive grains, and hit the abrasive grains to the supplying member to roughen the outer surface of the supplying member.
It is known that the surface treatment device of this kind has working efficiency higher than a sand blast device or shot blast device configured to hit abrasive grains to a supplying member by blowing out the abrasive grains by air pressure or water pressure.
Moreover, there has been known a development roller to convey a developer to a photo conductive drum, in which sand blast processing is provided on an outer surface of a development sleeve of the development roller to roughen the outer surface and V-shaped grooves are provided on the outer surface.
There is also proposed a so-called electro-magnetic blast which is configured to contain abrasive grains and a development sleeve in a containing tank, generate a rotational magnetic field to move the abrasive grains, excite the abrasive grains randomly by an electro-magnetic force operating between the rotational magnetic field and the abrasive grains and hit the abrasive grains to the development sleeve to roughen the outer surface of the development sleeve.
It is known that the electro-magnetic blast of this kind has working efficiency higher than a sand blast or shot blast configured to hit the abrasive grains to the development sleeve by blowing out the abrasive grains by air pressure or water pressure.
In the above-mentioned sand blast, hitting spherical glass beads to the outer surface of the development sleeve is proposed (for reference, see Patent Document 10).
Here, it is desired that the developer is adapted to be supplied from the development roller to the photo conductive drum uniformly, in the development roller, the surface treatment device, and the wire member used to provide a roughing treatment on the outer surface of the development sleeve.    (Patent Document 1): Japanese Patent Laid-Open No. 2000-194194    (Patent Document 2): Japanese Patent Laid-Open No. 2000-194195    (Patent Document 3): Japanese Patent Laid-Open No. 2004-198468    (Patent Document 4): Japanese Patent Laid-Open No. 2005-036534    (Patent Document 5): Japanese Patent Laid-Open No. 8-160736    (Patent Document 6): Japanese Patent Laid-Open No. 2003-305634    (Patent Document 7): Japanese Patent Laid-Open No. 2001-138207    (Patent Document 8): Japanese Patent No. 3486221    (Patent Document 9): Japanese Patent Laid-Open No. 61-38862    (Patent Document 10): Japanese Patent Laid-Open No. 2000-10336
However, in prior art as mentioned above, there is a first problem that not only the toner but also the magnetic carrier tend to be attached to the photo conductive drum 102 in the development area 103, although it is desired to attach only the toner of the toner and the magnetic carrier constituting the developer to the photo conductive drum. A magnetic force by the development roller 104, an electric force by the photo conductive drum 102, and a centrifugal force by the rotation of the development roller 104 are imparted to the magnetic carrier. The magnetic force is a force in a direction attracting the magnetic carrier to the development roller 104 whereas each of the electric force and the centrifugal force is a force in a direction drawing the magnetic carrier from development roller 104.
The magnetic carrier should be remain on the development roller 104 by the magnetic force, but, if a combined force of the electric force and the centrifugal force is larger than the magnetic force, the magnetic carrier is separated from the development roller 104 and attached to the photo conductive drum 102. This is a phenomenon referred to as “carrier attachment”.
If the magnetic carrier is attached to the photo conductive drum 102, the magnetic carrier together with the toner is moved to a transferred member or paper, there is a problem that this results in harmful influence for a transfer device or fixing device and low reliability of the image forming apparatus. In recent years, with the aim of high image quality of the image forming apparatus, small particulate magnetic carrier or low electric potential phenomenon has been reviewed in the development process. However, such a method is also insufficient to eliminate the carrier attachment.
To solve this problem, there has been proposed a device having high magnetic characteristic of development poles of the development roller 104 and adjacent different poles disposed downstream the development poles (for reference, see Patent Document 3). However, the device does not specifically disclose a relationship of magnetic flux densities of the development poles and the adjacent different poles. Generally, the magnetic flux density of the adjacent different poles is lesser than that of the development poles. If the magnetic flux density of the adjacent different poles is lesser than that of the development poles, A drop occurs in a combined distribution of magnetic flux density combining a distribution of the magnetic flux density of the development roller 104 in a normal direction and a distribution of the magnetic flux density of the development roller 104 in a tangent direction. Consequently, there is a problem that a low magnetic force occurs in a portion of the drop of distribution of magnetic flux density and therefore flexibility of the carrier attachment lacks.
On the other hand, there is a second problem that a particulate characteristic of the magnetic carrier is changed by filling in a surface of the magnetic carrier with an addition agent or friction of the surface of the magnetic carrier. The change of the particulate characteristic of the magnetic carrier causes an amount of the developer 101 picked up by the development sleeve 105 to change easily. Accordingly, there is a tendency that it is difficult to obtain high quality image throughout a long period for secular variation of the developer 101.
In the above-mentioned development sleeve 105 which includes an outer surface having a surface roughness of 10 formed by providing cutting or grinding process on the development sleeve 105 to maintain the axis of the development sleeve linearly, maintain inner and outer diameters of the development sleeve constantly, and maintain the sectional shape of the development sleeve in a constantly sized perfect circle or eliminate the wobble of the development sleeve, thereafter, by providing sand blast on the surface of the development sleeve, because very fine concave and convex portions are formed by the sand blast, the concave and convex portions of the outer surface wear gradually for secular variation. In the development sleeve 105 on which the sand blast is provided, because the concave and convex portions of the outer surface wear gradually for secular variation, an amount of the developer 101 picked up by the development sleeve is gradually reduced, as shown in FIGS. 25 and 26. In addition, the picked amount of the developer 101 is further reduced even by secular variation of the developer 101 as mentioned above.
Therefore, the use of the development roller 105 on which the sand blast is provided tends to lower image quality such as generation of variations in an image. Consequently, it is difficult to acquire high quality image throughout a long period in the development roller 105 on which the sand blast is provided.
Here, FIG. 25 illustrates an initial state of the outer surface of the development sleeve after using, and FIG. 26 illustrates a state varying across the ages after ten papers from initiation of use are printed. In FIGS. 25A and 26A, the developer 101 is shown by black mark, in FIGS. 25B and 26B, the developer 101 is shown by parallel diagonal lines.
In the development sleeve 105 on the outer surface of which the grooves are provided, friction of the grooves by secular variation is less, but there is a case that the wobble accuracy of development sleeve such as curvature of the axis, change of the inner and outer diameters of the sleeve, and generation of elliptical shape of the sleeve is lower than that of development sleeve formed by the sand blast, by a stress given in forming the grooves. In addition, when performing the cutting or grinding on the development sleeve after forming the grooves, burr occurs on an outer edge of each of the grooves. There is a case that the burr drops when forming an image to form a defective image and block the feeding of the developer. In this way, in the development sleeve 105 on the outer surface of which the grooves are provided, it is difficult to acquire an image having uniform density by low wobble accuracy.
Furthermore, even in the development sleeve 105 on the outer surface of which the grooves are provided, an amount of the developer 101 picked up by the development sleeve 105 is gradually reduced by the above-mentioned secular variation of the developer 101 (see FIGS. 27 and 28). Therefore, it is difficult for the development sleeve having the grooves to obtain high quality image throughout a long period.
Here, FIG. 27 illustrates an initial state of the outer surface of the development sleeve after using, and FIG. 28 illustrates a state varying across the ages after ten papers from initiation of use are printed. In FIGS. 27A and 28A, the developer 101 is shown by black mark, in FIGS. 27B and 28B, the developer 101 is shown by parallel diagonal lines.
The development sleeve 105 as disclosed in the Patent Document 5 includes an outer surface provided with a plurality of projection portions at ridge lines each having a polygonal shape and fine concave and convex portions provided on portions other than the projection portions, and a conductive resinous coating and a metallic treatment layer are provided on the outer surface to accomplish high accuracy and high durability. However, in the development sleeve 105 as disclosed in the Patent Document 5, when it is used continuously, there is a problem that the toner is adhered to the fine concave and convex portions to lower development ability or the like (for example, reduction of an amount of the developer 101 supplied to the photo conductive drum 102). In other words, it is difficult to acquire high image quality throughout a long period. In addition, as mentioned above, a troublesome process is required for forming the plurality of polygonal projection portions and the fine concave and convex portions other than the projection portions, thereby a cost for the process tends to increase.
Next, there is a third problem that the concave and convex portions formed by the sand blast process gradually wear to flatten by the developer or the like with increment of the number of printed papers or secular variation because the concave and convex portions formed on the outer surface of the development sleeve on which the above-mentioned sand blast process is provided are very fine. Consequently, in the development sleeve on which the above-mentioned sand blast process is provided, a conveyed amount of the developer is gradually reduced, and hence gradually thin images are formed.
Moreover, in the development sleeve as the supplying member having the outer surface provided with the V-shaped grooves, concavity and convexity of the V-shaped grooves are significantly larger than that of the concave and convex portions. In other words, because the V-shaped grooves formed on the outer surface of the development sleeve are very larger or deeper than the magnetic carrier in fineness, in the development sleeve having the V-shaped grooves, it is difficult to wear the V-shaped grooves, and hence the conveyed amount of the developer is not reduced as varying across the ages. However, in the development sleeve on the outer surface of which the V-shaped grooves are provided, because the developer conveyed by the V-shaped grooves is more than that conveyed by portions where the V-shaped grooves are not provided, variations of density of image are easy to occur in the formed image by the variations of the conveyed amount of the developer.
There is a fourth problem that a picked amount of the developer by the opposite ends of the development sleeve in the longitudinal direction is lesser than that of the developer by the central portion of the development sleeve in the longitudinal direction as known, when the outer surface of the development sleeve is formed in a uniform surface-roughness. In this case, if a desired image is printed on a recording paper, a thinner image than an image on a central portion of the paper is formed on the ends of the paper. In this way, there is a problem that variations occur in the image on the recording paper when the outer surface the development sleeve is formed in the uniform surface-roughness.
Furthermore, in the sand blast process using the glass beads, because the abrasive particles are larger than that used for a usual sand blast, the bending or distortion easily occurs in the development sleeve. In addition, in the sand blast process using the glass beads, because spherical glass beads are blown to the development sleeve, it is easy to generate periodicity in concave and convex portions of the outer surface of the development sleeve. Therefore, in the development sleeve on which the sand blast process using the glass beads is provided, the concave and convex portions formed on the outer surface are difficult to wear and the conveyed amount of the developer is not reduced by the secular variation. However, the variations in the density of the formed image easily occur by the periodicity generated in the concave and convex portions.